Abstracts

Kaulonia, an ancient Greek settlement (~700 to 389 B.C.), is positioned in a tectonically mobile setting on the Ionian coast of Calabria in southern peninsular Italy. Several extensive back-and-forth shoreline migrations have occurred along this coast since the mid-Holocene. These large-scale shifts, from 100 m landward of the present shoreline to 300m offshore, are recorded by tracing the lateral distribution of archaeological material and a distinct Holocene stratigraphic marker unit (beachrock-cobble sequence). Landward-directed (transgressive) shifts were induced during tectonically calmer periods when phases of relative sea-level rise prevailed. In contrast, a major seaward (regressive) coastal migration resulted primarily from an important ‘see-saw’ phase, with uplift landward and at the coast and a downward seafloor tilt. This Calabrian Arc tectonic event, leading to this offshore displacement in the mid- to late Holocene, is also recorded elsewhere in southern Italy. The approach used here, integrating geological and archaeological databases, serves to more precisely interpret settings where major nearshore changes have been driven largely by effects of structural mobility.

Outline

Author's notes

My sincere thanks are expressed to Drs. M.P.Bernasconi, M.T. Iannelli, S. Mariottini, and T. Toth for their valuable advice and assistance with the initial Kaulonia field study, contributions to geophysical and core data collection, and providing essential photographic documentation. Any errors introduced in this analysis that focuses on tectonic triggering of shoreline migrations at Kaulonia are the responsibility of the author. Technical assistance with the present study was provided by Ms. K. Carnes, Mr. T. F. Jorstad, and Ms. M. Richardson, National Museum of Natural History (NMNH). Constructive suggestions given by Dr. C. Vella and two anonymous reviewers helped improve the manuscript. Funding was obtained from the NMNH-Smithsonian Institution, and facilities in the field were made available through the kind auspices of the Soprintendenza, Beni Archeologici della Calabria (Dr. M. T. Iannelli) and the University of Calabria (Dr. M.P.Bernasconi).

Full text

1The world’s coastlines have been subject to major lateral displacement during the Holocene and, in the case of mid- and lower latitude settings, these shifts were primarily directed landward. Such transgressive shoreline migrations during this geologically recent period generally occurred as a result of progressive effects of natural events, primarily relative sea-level rise as a function of climate change and subsidence of seafloor surfaces. These effects, acting conjointly through time, have led to a shoreline advance landward and submergence of previously subaerially exposed late Pleistocene to Holocene shelf platforms and coastal margins. During this period, powerful episodic natural phenomena have also induced shoreline changes. These short-term events, numerous and varied, include marked climactic fluctuations, hurricane and strong storm surges, floods, tsunamis, earthquakes and fault displacement, volcanic activity, substrate sediment compaction and failure, and anthropogenic influences (Short 1999; Woodroffe 2002; and many others).

2However, while recognizing the overall importance of these latter effects, the present study focuses especially on the role of tectonic displacement that can locally disrupt the pattern of expected Holocene relative sea-level rise and landward coastal advance. The aim of this investigation is to provide insight on the specifics of Holocene shoreline changes through time in a highly mobile setting that has a long record of human occupation and settlement. There are many examples of such stretches identified on Mediterranean margins (Flemming 1969, 1998; Flemming & Webb 1986; Raban 1988; Morhange et al. 2005; Marriner & Morhange 2007). Attention herein is paid to a rather unusual coastline migration pattern in a long-inhabited sector at the archaeological site of Kaulonia located on the Ionian Sea coast of Calabria in southern peninsular Italy (Fig. 1). This sector is positioned within the Calabrian Arc, a tectonic setting that during much of the Quaternary denoted an active boundary between African and Eurasian plates (Figs. 1A, 2) and has been characterized by a record of considerable land displacement (numerous studies, including Westaway 1993; Bordoni & Valensise 1998; Parotto & Praturlon 2004; Moratti & Chalouan 2006).

3Recently, it has been determined that the coastal stretch examined here had been submerged in the early to mid-Holocene, and then subsequently became subaerially exposed seaward of Kaulonia (Stanleyet al. 2007). This latter time-span included the 300-year period when the settlement was occupied by the Greeks, starting about 2700 years ago (Orsi 1916; Mertens 1976; Iannelli 1985, 2005; Iannelli & Rizzi 1985; Treziny, 1989; Barello 1995; Parra 2001).

4Coastal and nearshore stratigraphic, geophysical and archaeological databases have recently been collected to better interpret the causes of shoreline shifts in this sector (data in Stanleyet al. 2007). These are integrated to determine why and when the Kaulonia shoreline shifted back-and-forth over a distance of at least 400meters, during a period of less than 5000 years in the mid- to late Holocene.

A, Location of Kaulonia (K) just north of Monasterace Marina (MM) on the Ionian Coast of Calabria, southern Italy (modified after Crescenti et al. 2004); the archaeological site is positioned within the Ionian forearc basin of the Calabrian Arc (Fig. 2B).B, Kaulonia was in Magna Graecia, a major sector of ancient Greek colonization. Localisation de Kaulonia

5Kaulonia was a rather modest-size Magna Graecia colony, one of several on the Ionian coast of Calabria (Randall-Maciver 1931; Schmiedt 1975). It was founded by the Achaeans, a people from the Peloponnesus, and perhaps also by settlers from Kroton (Crotone), another Greek settlement located to the northeast (Fig. 1B). Archaeological excavations at Kaulonia are positioned immediately north of the small coastal town of Monasterace Marina (MM in Fig. 1A). Kaulonia was conquered in 389 B.C. by Dionysius the 1st, tyrant of Syracuse, and its settlers deported to Locri, a colony positioned about 40 km to the SSW. A settlement was then rebuilt at the original Kaulonia site by the Brettii, a nomadic tribe in the 3rd century B.C., and was conquered once again, this time by the Romans in 205 B.C. The gentle arcuate headland immediately to the north of the site is known as Punta Stilo, or Cape of Columns (Fig. 3). It has had this name at least as far back as about 2000 years ago when the locality was cited by Pliny the Elder in his The Natural History. This suggests that columns may still have been visible to the Romans in this sector to about 2000 years ago, i.e. perhaps as long as 3 to 4 centuries after exile of the Greek settlers in 389 B.C.

6It is thus of special interest in this respect that numerous large fluted column sections and other archaeological materials were discovered by divers in the mid- to late 1980’s at water depths to 7 m up to 300 m offshore Kaulonia. The description, depth and geographic coordinates of each of the more than 100 features were carefully recorded (Iannelliet al. 1993; Lena & Medaglia 2002; Medaglia 2002a, b). Archaeologists working at the site suggested that the numerous columns had been manufactured along the coast and/or unloaded from ships sailing to this once-active trading center in Greek time. Until recently, archaeologists postulated that the configuration of the coastal strip on which the columns were originally placed, prior to coastal submergence, was a small, distinctive, low-lying hook-shaped cape (Iannelliet al. 1993; Lena & Medaglia 2002).

7However, more recent geoarchaeological analysis using data from geophysical and coring surveys (the reader is directed to high-resolution seismic profiles and lithological core logs shown in Stanley and others 2007) indicates that the seafloor on which the columns were discovered was actually only a small part of a broad arcuate (not small hook-shaped) headland that subsided after time of Greek occupation (STANLEY et al. 2007). Diving observations and numerous closely-spaced (<200 m apart) seismic profiles indicate that this headland was apparently without lagoon, or sufficiently deep waterway, or man-made port facilities to provide protected anchorage (Fig. 3). Moreoever, recent analysis also shows that a sector of the now-submerged surface, which currently lies at a depth of 5 to 7 meters below mean sea level (msl), had been partially covered by stratified sandstone originally formed along the beachline to foreshore zone during the latter half of the Holocene. This surface seaward of Kaulonia, comprising sandstone slabs, cobbles and boulders and archaeological material (Fig. 4A,B), appears to have been submerged completely beneath sea level during a time-span of approximately four to five hundred years. Based on artifacts recovered on the seafloor, the period of lowering lasted from roughly 400 B.C. near the end of Greek occupation to the time of Roman rule in about the 1st century A.D.

Paleogeographic scheme of the Kaulonia margin shows major Holocene coastal shifts: from former shoreline position (1), to seaward (2), and then return to the present coastline (3, 4). Dots represent mapped offshore archaeological material northeast of the Doric temple, Kaulonia’s major structure (after LENA & MEDAGLIA 2002). Cores MON I and II were recovered on and just landward of present coastal dunes. Interpretation of the offshore sector is based on dense coverage by geophysical lines (data in STANLEY et al. 2007). The time and spatial variations are discussed in text.Croquis géomorphologique présentant la mobilité des lignes de rivage à l’Holocène dans le secteur de Kaulonia.

8Bathymetric measurements (Iannelliet al. 1993; Lena & Iannelli 1996) show that the present seafloor surface in the study area extends fairly regularly seaward from the shoreline to a depth of ~6 meters. Here, it then levels or rises locally to ~3.5meters below msl (in offshore bar-like fashion), before once again deepening progressively seaward to depths of 20meters and more on the Ionian shelf. It is on a segment of this inclined offshore surface, in an area about 250 m by 500m, that large column sections, column bases, construction blocks, bollards and anchors were discovered (depicted as dots on Fig. 3), along with numerous potsherds and bronze, lead, and copper fragments (Lena & Medaglia 2002). The columns are dated stylistically to about 480-470 B.C. Archaeologists have determined that the large number of column sections (length to 113 cm, diameter to 80 cm) and other materials on the seafloor (Fig. 3) were not distributed haphazardly as a result of shipwrecks (Lena & Medaglia 2002). Rather, these and other archaeological features are positioned at, or proximal to, once-exposed coastal nearshore surfaces upon which they were worked and/or from which they were discharged from vessels. Larger column sections are usually positioned further seaward at greater depths than smaller sections. It has been suggested that the construction materials were at Kaulonia for the building of a temple or other major structure. However, excavations to date at the site have provided no evidence that such a project was completed (Orsi, 1916; Treziny 1989; Iannelli 1992, 1997; Parra 2001).

9Offshore archaeological material rests on, and is associated with, large slabs of stratified Holocene sandstone strata interpreted as beachrock cemented in the mid- to late Holocene (Stanleyet al. 2007). The sandstone, commonly with pebbles and cobbles (Fig. 4B, C), had once formed at, or possibly near, the spray zone (cf. Alexandersson 1972; Dalongeville 1984; Bernier & Dalongeville 1988; Fouacheet al. 2005) and/or the shallow submerged sector of a former coastline (cf. Milliman 1974). These slabs are surrounded by rounded cobbles and large boulders (Fig. 4A) of igneous and metamorphic lithologies originally derived from headwaters of the Assi River in the Serre mountains (Ibbeken & Schleyer 1991). The now much smaller stream presently flows to the coast about 500 m north of the Kaulonia site. The most recent paleogeographic reconstruction (Fig. 3) has been compiled on the basis of geophysical survey profiles offshore and analyses of cores (length to 20m) collected on land. It appears that ships arriving at the site were most commonly anchored close to shore and/or beached. Moreover, the Assi River at the time of Kaulonia’s existence flowed southeast of its present location (Fig. 3), and vessels were thus probably also secured near, or within, the channel mouth when the river was not in flood stage (Stanleyet al. 2007).

10Recent geological evolution of the Kaulonia coastal margin and its shoreline migrations are determined by using a distinct litho-stratigraphic marker (beachrock-and-cobble horizon) ranging from mid- to late Holocene age, depending on its location seaward (Fig. 4B) or landward (Fig. 4C) of the shoreline. This unit can be traced laterally for a distance of at least 400m, from two cores collected on land behind dunes, about 100 m shoreward of the present coastline, to offshore sectors at least 300 m seaward of the shoreline (Fig. 3). Throughout this broad area, the marker unit presents a generally consistent thickness (~1m; Fig. 4B, C) and lithology. Beachrock sandstone is formed mostly of Assi River detrital mineral grains cemented by high Mg-calcite and dolomite, and pebbles and cobbles are of Assi headwater metamorphic and igneous composition. Radiocarbon dating of the carbonate cement indicates that the beachrock unit recovered in core MON I (position of maximum ingression shown in Fig. 3), lying ~2 m beneath sediment with Greek artifacts, is of mid-Holocene (pre-4500 yrs B.P.) age (Stanley et al. 2007). Radiocarbon analysis of the moderately to poorly consolidated stratified beachrock sandstone provides variable ages, including some to early Holocene. Samples recording such older ages likely indicate dates of introduced reworked (by groundwater, run off and other) and weathered carbonate and dolomite that forms the cement rather than the more recent time of beachrock formation.

11Archaeological examination of Greek materials discovered offshore indicates their ages as being approximately 2500 years B.P.These construction features are commonly associated with the sandstone-conglomerate stratigraphic marker sequence presently at depths of 5 to 7meters below sea level (Figs. 3, 4B). Where found, it is of note that both archaeological material and marker unit offshore lie at least 2 to 3 m deeper than can be readily accounted for by (1) recent strong coastal, shoreface and seafloor erosion effects and (2) world sea-level stand and rise during the past 2500 years (cf. Fairbanks 1989; Lambeck & Purcell 2005). A third component affecting depth, (3) sea-floor subsidence of 2.5 ± 0.5 m or more during the past ~2500 years, appears to best explain the extra lowering of seafloor surface between the coast and inner shelf. This recent subsidence phenomenon alone would account for an averaged Holocene long-term mean submergence rate of nearly 1mm/year.

12It is noted that this submergence rate value is quite similar to the rate of averaged long-term Quaternary uplift measured landward of the coast in this Calabrian sector, where a land surface rise of ~0.9mm/year and greater has been recorded (Westaway, 1993; Dumas and Raffy, 1994; Dumaset al. 1995; Bordoni & Valensise 1998; Ferrantiet al. 2006). These different authors determine uplift landward of the Kaulonia coast by measuring the present elevation of terraces of Pleistocene and Holocene age that had once formed at or close to sea level. Particularly valuable in this respect are marine terraces formed during the climatic optimum or maximum transgressive, known historically as the Tyrrhenian highstand, dated at about 125,000 years ago and most closely correlated with substage 5e of the oxygen isotope record. For example, terrace levels in a proximal sector of southern Calabria (hills behind Ardore Marina and west of Soverato, denoted as sites 65 to 74 in Fig. 5) have been uplifted to elevations ranging from 90 to 113 m above msl (Cosentino & Gliozzi 1988; Bordoni & Valensise 1998).

Site locations (small numbers) of Tyrrhenian marine terraces on land and their elevation in meters above msl (bold larger numbers) in southern Italy. K=Kaulonia. Map is modified from BORDONI & VALENSISE (1998), where these authors provide data (their Table 1) on terrace elevations and ages, and reference sources from where data are derived.Altitudes des terrasses tyrrhéniennes.

13Seaward, the closely-spaced high-resolution geophysical profiles obtained in a 1 km2 area just off Kaulonia (Stanleyet al. 2007) record the presence of a distinct sub-bottom reflector that lies 1 to 4 m beneath the present sediment-water interface. This now-buried dense acoustic reflector is identified as the stratified sandstone-conglomerate marker unit (Fig. 4B) that forms the substrate upon which rest archaeological materials (Iannelliet al. 1993), and which can be traced between the shallow nearshore and inner shelf. Unfortunately, after 1991, both distinct horizon and associated archaeological features on the seafloor were almost entirely covered by storm-reworked sands (locally to 4 m thick) that had been driven shoreward (Dr. S. Mariottini, Associazione Culturale Kodros, 2006, personal communication based on dive records). A comparable unit, about 1.0 to 1.5 m thick and comprising sandstone welded upon conglomerate, was observed as a 100m-long subaerial exposure near the base of dunes north of Kaulonia’s temple (Fig. 4C) and also in sediment cores (elevations to near and above msl) recovered farther inland behind the dunes (MON I and II, in Fig. 3). This would account for an incline of about 1:40, from +2 m above msl on land to -7 m offshore over a distance of less than 400m.

14It has recently been observed that the base of the Doric temple at Kaulonia is formed of stratified carbonate-cemented sandstone similar lithologically to the one in the stratigraphic marker unit discovered both on land and offshore. It appears that this temple base material is formed of cut beachrock blocks I believe were obtained locally by the Greek settlers, i.e. most probably from the coast seaward of the temple (see sandstone slabs in Figs. 3, 4B; Stanleyet al. 2007). Beachrock sandstone at Kaulonia is similar to that identified on many Mediterranean coasts (Alexandersson 1972; Dalongeville 1984). Of note are those distributed along the Calabrian Ionian coastal margin and identified as late Holocene in age (Pirazzoliet al. 1997).

15To determine the causes of shoreline reversals at Kaulonia, it is useful to assess several salient aspects of local stratigraphy and tectonics.

16• Chrono-stratigraphic interpretations that take into account the spatial and temporal distribution of the inclined sandstone-conglomerate marker unit serve to define coastal-inner shelf paleogeographic changes through time and measure migrations of Kaulonia's coastline over a distance of 400 m since the mid-Holocene. The nearshore marker unit that defines coastal shifts from ~4500 to 2500 yrs B.P.is viewed as a time-transgressive stratigraphic horizon. It indicates that the mid-Holocene shoreline had shifted landward, submerging the coastal margin to ~100 m inland of the present shoreline at about 5000-4500 yrs B.P.This was followed by a seaward-directed migration that then subaerially re-exposed the coastal margin at some time between ~4500 years B.P.and early occupation of the site by the Greeks about 2700 years ago (coastal shift 1 to 2 in Fig. 3). After that time, Kaulonia’s coastal margin, partially covered by the Greek column sections and other construction material, was subject to a second phase of Holocene submergence. This most recent event is dated after exile of the Greek population in the 4th century B.C., and was probably underway by Roman time in the 1st century A.D. (to 3 in Fig. 3). Transgression of the shoreline westward to its present position continued during most of the past 2000 years (to 4 in Fig. 3).

17• A tectonic axis positioned close to the present coastal margin (Fig. 2B) is suggested by the measured near-equivalent averaged rates of land uplift (0.85 - 0.90mm/year or more) and offshore submergence (~1.0mm/year). It appears that a geologically recent 'see-saw' motion (upward on land, downward offshore) took place in the proximity of the study area, with an axis positioned at or near the coast (Fig. 7B). None of the 48 high-resolution, shallow penetration geophysical profiles (37 kms of seismic line) that cross the entire seaward sloping surface between the shoreline and 1000 m offshore Kaulonia record major faults or other structural offset (Stanleyet al. 2007, their figures 4-6). This suggests that late Holocene seafloor submergence occurred largely as the result of a downward-directed tilt motion, with minimal offshore offset, at least within the upper ~10 m of strata. Seismic activity then and subsequently may have caused some downslope and seaward displacement of anthropogenic structures such as column sections.

18• The terrain on land, between the sector that extends from just behind the dunes at the coast proper to hills that back Kaulonia, presents a markedly different configuration (Figs. 5, 6). Sequences of Pliocene and Quaternary deposits are characterized by numerous structural offsets and faults, and also gravitative downslope slide and slump displacement (carta geologica della calabria 1968; Patacca & Scandone 2004). Recent structural motion, for example, is recorded by Quaternary alluvial sediment strata that form the terrace-like (tectonic, non-fluvial) platforms that abruptly rise above the beach and whose stratal surfaces are inclined (Fig. 6A, B). The top of the plateau-like tectonic feature at the back-beach ranges from 8 m to 10 m in elevation above msl (Fig. 6C), and its steep seaward face is partially fronted by dune sand. Exposures in back-beach dunes and terrains just behind the dunes, within 100 m of the present shoreline, reveal displaced and offset sediment sequences that comprise both alluvial (some mud-rich) and nearshore (sand-rich) strata (Fig. 6A, B). It appears that Kaulonia's coastal evolution during the Holocene has involved episodic uplift resulting in an irregular terrain morphology of sediment strata landward of the coast (Fig. 6C, D). In marked contrast, the more continuous seafloor surface and subbottom Holocene strata offshore (seismic profiles in Stanleyet al. 2007) appear modified more by a downward tilt motion seaward than by a series of major fault breaks as noted on land.

Structurally displaced terrain at the Kaulonia coast. A, B, Steep back-beach terrain in vicinity of the Doric temple (~10 m relief), formed of alluvial sediment partially fronted by dune sand. Arrows in A identify dipping (perhaps slide) bedding. C, View from offshore toward hill top (40 m elevation) on which lighthouse was built behind and north of the Doric temple; dissected and step-like topography, formed by marine and terrigenous Pleistocene and Quaternary deposits, record faulting and slump displacement. Also evident is tilted offset surface of the 10-m tectonic terrace that rises above the back-beach. D, View toward southeast, showing tectonically offset Pliocene and Quaternary terrain between base of lighthouse hill and the coastline (distance of ~260 m); arrow in distance points to base of Doric temple. Coast-parallel road SS-106 provides scale.Mobilité tectonique dans le secteur de Kaulonia.

19Integration of the above observations is summarized here by a series of simplified diagrams (Fig. 7). The nearshore stratigraphic marker (sandstone-cobble unit) indicates that the shoreline had transgressed to a position 100 m landward of the present coast by 4500 years ago (Fig. 7A, 1). This key unit then records a major shoreline regression to at least as far as ~300 m seaward of the present coast by about 2500 years ago (Fig. 7B, 2). Finally, coastline migration reversal began once again in Roman time (Fig. 7C, toward 3), with the dominant landward shift (transgression) continuing during the past two millennia until the shoreline reached its present position (Fig. 7C, 4). The back-and-forth migration during the mid- to late Holocene is attributed primarily to uplift and a change in slope inclination of the seaward-tilted surface off the present coast. During the early to mid-Holocene, the gentle and relatively uniform offshore sloping surface induced the shoreline to migrate landward primarily as a result of relative sea-level rise (Fig. 7A). However, when the seafloor was subsequently uplifted near shore and surface inclination increased, the shoreline began to reverse direction seaward (Fig. 7B).

20As the coastline migrated back offshore, the previously submerged coast to inner shelf sector once again became subaerially exposed, and thus readily accessible to the Greeks settling at Kaulonia. Exposed beachrock in the coastal area (Fig. 7B) was exploited by the settlers. For Kaulonia’s temple base construction alone, it is calculated that the cut beachrock material would have covered a surface area of at least 1250m2. This would be equivalent to a shore-parallel sandstone exposure 100 m long by 12.5m wide and 40 cm or more thick (Stanley et al. 2007). Thus, once exposed and readily visible along the beach and foreshore, this deposit may well be one of the major reasons the locality near the Assi River was originally selected for colonization by the Greeks.

21In a final phase, the shoreline once again migrated progressively landward. This has taken place during stabilization of the seafloor surface elevation and its inclination, and a relative sea level rise that continued in Roman time (Fig. 7C, 3). The general quiescence phase appears to have persisted until the present (Fig. 7C, 4).

Simplified series of sketches to show use of archaeology, sedimentology and stratigraphy to explain major coastline shifts (1) to (4) at Kaulonia (see Fig. 3). Noted are lateral displacement of the beachrock-cobble unit over a distance of 400 m in this mobile sector of the Ionian forearc basin of the Calabrian Arc (Fig. 2B). A, Early to mid-Holocene transgression (black arrow) and westward coastline position (1), due primarily to effects of relative sea-level rise. B, Reversed mid- to late Holocene seaward migration of the shoreline (regression, black arrow) from (1) to (2) during mid- to late Holocene; this was primarily induced by a major tectonic uplift phase and ‘see-saw’ motion at or very near coastal axis. C, Post-Greek shoreline migration once again shifted landward, largely the result of rise in relative sea-level. No beachrock forms at present. Further explanation in text.Trois principales phases de mobilité des rivages à Kaulonia depuis l’Holocène moyen.

22Increase of seafloor elevation and inclination was likely induced by one or several powerful, regionally important tectonic pulses in the mid- to late Holocene. Geological studies in this region (Gaspariniet al. 1982; Dumas & Raffy 1994; Dumaset al. 1995; Pirazzoliet al. 1997), and in more distal parts of southern Italy (Amato & Montone 1997; Cucci 2005), recorded evidence of increased regional arching and marked uplift that caused tectonic instability and deformation in the Calabrian Arc during this time-span. These caused increased uplift on the landward side of the coast in the study area and, concurrently, a substantial amount of offshore tilt. Since time of exile of the settlers from Kaulonia after ~2400 B.P., the local coastal margin has generally been affected by less powerful tectonic phases of landward rise and somewhat more gentle submergence of the offshore sector. These somewhat more stable conditions during the past 2000 years have resulted in an increased effect of relative sea-level rise rather than primarily of tectonics, thus causing the coastline’s landward shift to its present position.

23Holocene coastal evolution in the world’s low and mid-latitudes is most often characterized by marine transgression due largely to relative sea-level rise but, as reported in the present study, not all coastlines in these regions have migrated consistently or uniformly landward. This investigation demonstrates that marine regressions occurred on some coastal margins where effects of significant tectonic displacement exceeded those induced by more progressive eustatic or relative sea-level rise. The offshore coastline migration recorded at Kaulonia in the Calabrian Arc during the mid- to late Holocene was a response to increased structural mobility that affected this margin located within the mobile Ionian forearc basin. Geologically recent uplift pulses raising terrains landward of and at the shore most likely was the major cause of re-emergence of Kaulonia’s earlier submerged coastal margin. It is expected that this type of tectonically activated coastal regression also occurred at various times during the Holocene in other structurally mobile margins of the Mediterranean, such as in the Hellenic and Cyprus arc settings.

24There is growing awareness of the need to improve protection of coasts, especially in Mediterranean sectors where population growth and a large number of municipal and industrial projects have considerably increased. Engineers and coastal managers tend to focus primarily on vulnerable, moderately stable, low-lying margins, while some equally precarious nearshore sectors subject to major tectonic displacement have received substantially less attention. The major point herein is that valuable insight on shoreline changes is to be gained where information on geological structural mobility is integrated with records of long-term human activity. This geoarchaeological approach also serves to better devise and implement more effective long-term coastal protection measures.

Flemming, N.-C., (1969), Archaeological evidence for eustatic change of sea level and earth movements in the Western Mediterranean during the last 2,000 years, The Geological Society of America Special Paper 109, p.1-125;

List of illustrations

Title

Fig. 1

Caption

A, Location of Kaulonia (K) just north of Monasterace Marina (MM) on the Ionian Coast of Calabria, southern Italy (modified after Crescenti et al. 2004); the archaeological site is positioned within the Ionian forearc basin of the Calabrian Arc (Fig. 2B).B, Kaulonia was in Magna Graecia, a major sector of ancient Greek colonization. Localisation de Kaulonia

Paleogeographic scheme of the Kaulonia margin shows major Holocene coastal shifts: from former shoreline position (1), to seaward (2), and then return to the present coastline (3, 4). Dots represent mapped offshore archaeological material northeast of the Doric temple, Kaulonia’s major structure (after LENA & MEDAGLIA 2002). Cores MON I and II were recovered on and just landward of present coastal dunes. Interpretation of the offshore sector is based on dense coverage by geophysical lines (data in STANLEY et al. 2007). The time and spatial variations are discussed in text.Croquis géomorphologique présentant la mobilité des lignes de rivage à l’Holocène dans le secteur de Kaulonia.

Site locations (small numbers) of Tyrrhenian marine terraces on land and their elevation in meters above msl (bold larger numbers) in southern Italy. K=Kaulonia. Map is modified from BORDONI & VALENSISE (1998), where these authors provide data (their Table 1) on terrace elevations and ages, and reference sources from where data are derived.Altitudes des terrasses tyrrhéniennes.

Simplified series of sketches to show use of archaeology, sedimentology and stratigraphy to explain major coastline shifts (1) to (4) at Kaulonia (see Fig. 3). Noted are lateral displacement of the beachrock-cobble unit over a distance of 400 m in this mobile sector of the Ionian forearc basin of the Calabrian Arc (Fig. 2B). A, Early to mid-Holocene transgression (black arrow) and westward coastline position (1), due primarily to effects of relative sea-level rise. B, Reversed mid- to late Holocene seaward migration of the shoreline (regression, black arrow) from (1) to (2) during mid- to late Holocene; this was primarily induced by a major tectonic uplift phase and ‘see-saw’ motion at or very near coastal axis. C, Post-Greek shoreline migration once again shifted landward, largely the result of rise in relative sea-level. No beachrock forms at present. Further explanation in text.Trois principales phases de mobilité des rivages à Kaulonia depuis l’Holocène moyen.